1. Field of the Invention
This invention relates generally to hand tools for scoring, slitting and stripping insulative polymeric cable jackets from sheathed electric cables, strip heaters, and the like.
2. Background of the Invention
While there are a wide variety of cable stripping hand tools presently available, none of them have been found to work well for stripping the jackets of self-regulating heating cables, for example. Therefore, general purpose utility, craft or pocket knives have frequently been used for stripping off protective jackets of such cables to enable access to, and electrical connections to be made to an underlying metal braid layer and to the electrical conductors of the strip heaters. While these general purpose cutting tools have been known and widely used for many years, a high level of user skill and experience is required to use such tools safely and successfully, particularly without causing scoring, cutting or other unwanted damage to the underlying metal braid layer, base jacket layer or the conductors themselves. For example, when using a general craft knife or pocket knife it is easy to score and damage the underlying braid layer while cutting through the outer sheath or jacket, since there is no effective regulation of cutting depth other than the skill of the knife""s user. In some instances the conductors may be damaged while scoring the base jacket. In addition, there remains a high risk of personal injury to the user from inadvertent cutting because of the relatively large amount of exposed cutting blade edge when conventional general purpose knives and hand tools are used.
Specialized tools have been proposed for cable slitting. For example, U.S. Pat. No. 4,433,484 to Antisdel et al. entitled xe2x80x9cCable Stripperxe2x80x9d shows an elongated two-part tool using standard razor blades. One of the blades is exposed within a groove at one end of the tool for scoring the cable jacket, while another blade is exposed within a hook portion at an opposite end of the tool. The hook portion does not include any contouring to aid separation of the cable edge during slitting. Also, the cable scoring blade edge is directly exposed to the user, and the indicated manner of use has the user""s thumb placed nearly or directly over the cable scoring blade during the sheath scoring operation, leading to potential personal injury to the thumb.
Another tool for stripping a cable is illustrated in U.S. Pat. No. 4,189,799 to Litehizer, Jr., entitled xe2x80x9cCable Stripping Toolxe2x80x9d. The disclosed device includes blades for penetrating and tearing off the cable sheath and then for stripping insulation off of ends of individual wires of the cable. The insulation jacket is not always completely removed at the cable end being prepared for connections.
A fairly complicated and expensive two-part tool for stripping cable jackets and wire insulation is shown in U.S. Pat. No. 5,337,479 to Ducret, entitled xe2x80x9cCable and Wire Stripperxe2x80x9d. This particular tool includes a thumb screw enabling adjustment of cutting depth of the blade used for both scoring and slitting, but does not appear to have a size or overall shape which facilitates easy or comfortable grasping in the use""s hand during usage.
Another hand-held tool for stripping off a plastic sheath covering a cable is described in U.S. Pat. No. 5,142,780 to Brewer, entitled xe2x80x9cElectric Cable Stripping Tool with Clawxe2x80x9d. This tool includes a dulled claw which is used to pierce through the outer plastic sheath, and a crescent shaped blade edge including a parting shoe to facilitate slitting operation. Neither the claw nor the crescent shaped blade is effectively shielded to protect the user from being inadvertently cut or punctured.
Other hand-held tools for stripping off cable sheaths are shown for example in U.S. Pat. No. 3,946,487 to Bieganski, entitled xe2x80x9cTools for Cuttingxe2x80x9d; U.S. Pat. No. 3,881,249 to Cox, Jr., entitled xe2x80x9cCable Stripperxe2x80x9d; U.S. Pat. No. 4,472,877 to Undin et at., entitled xe2x80x9cTool for Removing Insulation from Cablesxe2x80x9d; U.S. Pat. No. 4,081,871 to Knuth, entitled xe2x80x9cElectrician""s Wire Stripping Toolxe2x80x9d; and U.S. Pat. No. 4,426,778 to Christie, entitled xe2x80x9cDevice for Stripping Wire and Cablexe2x80x9d. A tool head for an automated cable stripper is shown in U.S. Pat. No. 4,543,717 to Luka, entitled xe2x80x9cCable Stripperxe2x80x9d.
While such prior approaches appear to have been reasonably effective for their intended purposes, they were not without drawbacks. Some of the approaches featured and required custom blades, or special mechanisms and arrangements enabling the blade to be moved into cutting position or adjusted for cutting depth, or retracted after use. Some did not inherently provide any protection against unwanted exposure to cutting during use or handling. And, many of the prior approaches did not combine the features of relative simplicity, ease of manufacture at low cost, and ease of use, into a single hand-held cutting instrument.
This invention relates to improvements in hand-held devices for stripping polymeric jackets of cables, such as electrical power cables, communications cables, fiber optic cables and self-regulating heating cables. An elongated and substantially flat plastic sheath cutting and slitting hand tool following the principles of the present invention provides a scoring function and a slitting function in a manner that improves upon prior approaches. For example, the scoring function presents a scoring blade edge of a low cost standard craft knife blade when the tool is held in a first orientation enabling the user to score the plastic sheath to a controlled depth slightly less than the sheath thickness along e.g. a radial score line. A cover structure effectively covers the scoring blade to protect the user from being cut accidentally. The slitting function is used when the tool is turned over to a second orientation in the hand and after the cable at the radial score line has been manipulated to sever completely the plastic sheath. Then, the slitting function featuring a guiding shoe contoured to resemble a hook or plow guides a slitting blade along the cable sheath during a lengthwise slitting operation. The slit section of plastic jacket can then readily be removed.
Hand tools in accordance with the present invention are particularly useful for stripping the polymeric protective and insulating jackets of self-regulating heating cables of the type sold by Raychem HTS, of Menlo Park, Calif. Self-regulating heating cables frequently have unique cross-sectional shapes and multilayer construction. The tools of the present invention may be used with self-regulating heating cables of a broad range of sizes, shapes and jacket materials.
In accordance with principles of the present invention, a plastic sheath scoring and slitting hand tool is provided for cutting and slitting a cable sheath. The tool includes a generally flat, elongated body forming a handle portion adapted to be grasped by the hand, and a tool portion angling outwardly from the handle portion at a predetermined obtuse angle. The tool portion includes a covered a sheath-scoring blade for radially scoring a plastic sheath when the handle portion is grasped in the first orientation. In this regard the sheath scoring blade has a cutting edge following a predetermined contour such as straight or convex, and the tool portion at the blade includes opposed shoulders following the convex contour of the cutting edge in order to establish a predetermined maximum scoring-cutting depth set to correspond generally to thickness of a cable sheath layer to be scored. Further, the tool portion of the body has a generally flat sheath engaging and slitting edge portion defining a sheath slitter for engaging, spreading and slitting the plastic sheath lengthwise when the handle portion is grasped and drawn along the sheathed cable from a score line of the sheath made by the sheath scoring blade. In this regard the sheath slitter includes a slitting blade having a generally straight slitting edge forming an oblique angle facing the handle portion and a contoured sheath-spreading foot at an outer end of the slitting blade for engaging an underside, and spreading apart facing edges, of the cable sheath undergoing slitting by the slitting blade as the hand tool is drawn along a length of cable during a cable slitting operation. A number of different geometries and arrangements for the cable scoring feature are described.
These and other objects, advantages, aspects and features of the present invention will be more fully understood and appreciated by those skilled in the art upon consideration of the following detailed description of preferred embodiments, presented in conjunction with the accompanying drawings.